1. Field of the Invention
This invention relates to a printing device capable of ejecting a liquid mixture composed, for example, of ink and a diluent toward a recording medium, and more particularly to an improvement in arrangement of nozzles.
2. Description of the Related Art
So-called on-demand-type ink jet printer is adapted to form print images on a recording medium such as paper or film by ejecting ink droplets through nozzles in response to recording signals supplied to the printer. Recently, the ink jet printer of such a on-demand type has been rapidly prevailed due to its compactness or low manufacturing cost.
U.S. Pat. No. 5,371,529 previously filed by the present applicant, discloses the printer of such an on-demand type in which a gradation of recorded images is achieved by mixing ink and a transparent solvent as diluent at adequate proportions with each other immediately before ejection thereof. In such a printer, a concentration of the print images can be varied every recording dot, so that the printer is advantageous for obtaining a high quality duplicate of natural images such as photographs.
The printer is of a so-called intermixing type in which ink and diluent are mixed together in an interior of the ejection nozzle.
Meanwhile, in the conventional intermixing type printing device, there has been a problem that undesired mixing of ink and diluent and, therefore, mutual diffusion proposed, in the afore-mentioned U.S. Pat. No. 5,371,529, the printer in which a one-way valve manufactured according to an electroforming method is disposed in a boundary region between ink and diluent so as to prevent occurrence of the mutual diffusion therebetween during the stand-by period.
However, it is often difficult to completely separate ink from diluent during the standby period only by the arrangement of such a one-way valve. In addition, The one-way valve has another problem that its manufacturing cost is high.